Two-pedal hydraulic braking system

ABSTRACT

A two-pedal hydraulic braking system incorporates two separate pedal-operated master cylinders. Each master cylinder includes a pressure space in a cylinder bore in front of a pedal-operated piston working in the bore. The pressure spaces are connected by a transfer connection which permits fluid to pass between the pressure spaces to compensate for uneven wear of the linings of brakes on opposite sides of the vehicle. Normally communication between each master cylinder and the transfer connection is cut off by a normally closed valve which is opened when the piston is moved axially in the bore.

United States Patent Ingram Feb. 8, 1972 i [54] TWO-PEDAL HYDRAULICBRAKING SYSTEM [72] Inventor:

[73] Assignee: Girling Limited, Tyseley, Birmingham, En-

gland [22] Filed: Mar. 31, 1970 [21] Appl.No.: 24,195

Brian Ingram, Warwickshire, England [30] Foreign Application PriorityData May 8, 1969 Great Britain ..23,442/69 [52] US. Cl ..60/54.6 P,60/546 E, 188/345, 188/358, 60/545 P [5|] Int. Cl ..Fl5b 7/00 [58] Fieldof Search .,60/54.5 P, 54.5, 54.6 E, 54.6 P, 60/52 H; 188/345 [56]References Cited UNITED STATES PATENTS 3,120,244 2/1964 Hahn ..60/54.5 E

3,520,577 7/1970 Moyes ..188/345 2,992,533 7/1961 Hodkinson ...60/54.6 P3,044,268 7/ 1962 Harrison ..60/54 6 3,421,320 1/1969 Kershner.....60/545 E 3,376,078 4/1968 Brace et a1. ...60/54.5 E 3,345,112 10/1967Kershner ..60/54.5 E

Primary Examiner--Edgar W. Geoghegan Assistant ExaminerA. M. Z u pcicAttorney-Imirie 8L Smiley [57] ABSTRACT A two-pedal hydraulic braking.system incorporates two separate pedal-operated master cylinders. Eachmaster cylinder includes a pressure space in a cylinder bore in front ofa pedal-operated piston working in the bore. The pressure spaces areconnected by a transfer connection which permits fluid to pass betweenthe pressure spaces to compensate for uneven wear of the linings ofbrakes on opposite sides of the vehicle. Normally communication betweeneach master cylinder and the transfer connection is cut off by anormally closed valve which is opened when the piston is moved axiallyin the bore.

11 Claims, 4 Drawing Figures PATENTED FEB 818?? sum 2 0 4 A mm r w m m mr 3 T m m w l I NW ww 1 R w Q mm m w Q m mu 3 R E S r m I t m Q, d I M rmm I r v x mm mm I 1 @m Q WEE %i a .7 N J2 Q 9 PATENTEU FEB 8'97? sum 3or 4 3.640.067

. a mm r Wm QM m mm 4; m m mm, 1 @V l 1 T 1 mm a a W. @K \3 I m1 5 mm Wwmm W m 3 v \b N \NV I A WW). Q I P Q 1 K mm mm I 3 m Q m mm Q m mm c mmi Q a TWO-PEDAL HYDRAULIC BRAKING SYSTEM SPECIFIC DESCRIPTION Thisinvention relates to a new or improved two-pedal power operatedhydraulic braking system of the kind commonly used on agriculturaltractors and like vehicles in which brakes on opposite sides of thevehicle are adapted to be applied by fluid from separate mastercylinders each actuated by its own pedal.

The pedals can be operated simultaneously for retarding the vehicle orseparately for steering.

Owing to the nature of the work done by the vehicle the linings of thebrakes on one side of the other vehicle wear more rapidly than those onthe other side and to apply the brake uniformly it is essential that,when the pedals are operated simultaneously equal fluid pressures areapplied to the brakes on opposite sides of the vehicle.

According to our invention in an hydraulic braking system of the kindset forth each master cylinder comprises a positively actuated pistonworking in a bore in the cylinder body, a first passage in the cylinderbody adapted to be connected to a source of fluid under pressure andopening into a pressure space in front of the piston, a normally closedfirst valve controlling the first passage, a second passage in thecylinder body adapted to be connected to a reservoir for the pressuresource and leading into the pressure space, and a normally open secondvalve controlling the second passage, the pressure spaces of the twomaster cylinders being connected by a transfer connection which isisolated from the pressure spaces of both cylinders by normally closedtransfer valves which are opened upon movement of the pistons in brakeapplying directions.

Preferably each transfer valve is opened in a predetermined sequenceafter closure of the second valve has been effected, and before openingof the first. When one pedal only is operated toadvance the piston inone master cylinder, after the closure of the second valve, the transfervalve is opened and the transfer connection is then in communicationwith the pressure space in front of the piston, but fluid can not passfrom the pressure space to the pressure space of the second mastercylinder as the, transfer valve in the second master cylinder remainsclosed.

If both pedals are operated simultaneously to advance the pistons inboth master cylinders the transfer valves in both cylinders are openedand fluid can pass freely from the pressure space of one master cylinderto the other to compensate for uneven wear of the'friction linings ofthe brakes on opposite sides of the vehicles.

Some braking systems incorporating our invention are illustrated in theaccompanying drawings in which:

FIG. 1 is a schematic layout of an hydraulic braking systemincorporating two pedal-operated master cylinders;

FIG. 2 is a schematic layout similar to FIG. 1 but including somemodifications;

FIG. 3 is a schematic layout of a further modified braking system; and

FIG. 4 is a longitudinal section through a practical form of mastercylinder.

In the braking system illustrated in FIG. 1, two master cylinders and 11are arranged in side-by-side relationship. Each master cylinder 10, 11comprises a pedal-operated main piston assembly 12 working in a bore 13in a body 14. A pressure space 15 is defined between the inner end ofthe piston assembly 12 and the opposite end wall of the bore 13.

A reservoir 16 for hydraulic fluid is in communication through a line 17with the pressure space 15 in each cylinder through a spring loadingtipping valve 18. Each tipping valve 18, in the inoperative positionshown, is nonnally held in an open position by the engagement with thestem of the valve 18 of the rear end of a cage member 19 carried by thepiston assembly 12 in each respective cylinder.

The reservoir 16 provides a supply of fluid for a power operated pump(not shown) which is adapted to charge an hydraulic accumulator 20. Theaccumulator 20 is connected to the pressure space 15 of each cylinderthrough a common branched line 21 but the supply of hydraulic fluid toeach pressure space is normally cut off by a normally closedspringloaded tipping valve 23. Each tipping valve 23 is provided with a stemwhich extends into the path of the inner end of the respective cage 19and from which it is normally spaced.

In accordance with our invention the pressure spaces 15 of the mastercylinders are interconnected by a line 24 through which flow ofhydraulic fluid between the pressure spaces 15 is normally prevented bya normally closed spring loaded transfer valve 25 of the tipping typelocated in each master cylinder. Each transfer valve 25 is located at anintermediate point between the inner end of the cage and the tippingvalve 23 and has a stem which extends into the path of the inner end ofits respective cage and from which it is normally spaced.

The pressure space 15 of each master cylinder is provided with aconnection 26 to the brake on wheels on one side of the vehicle.

In the fully retracted position of both pistons 12, as shown in thedrawings, both tipping valves 18 are held in open positions byengagements with their stems of the cages 19 so that each pressure space15 is in communication with the reservoir 16.

When the piston assembly 12 of one master cylinder for example themaster cylinder 10 is advanced by operation of its pedal a short forwardmovement is sufficient to cause the cage 19 to be moved out ofengagement with the stem of the tipping valve 18 and allow the valve toclose under the action of its spring loading. Further movement of thepiston assembly 12 causes the cage 19 to engage with the stem of thetransfer valve 25 which is opened to place the pressure space 15 incommunication with the line 24.

However, if the piston assembly 12 of the other master cylinder 11 hasnot been advanced, the transfer valve 25 of the master cylinder 11remains closed so there can be no transfer of fluid between the pressurespaces 15 of the two master cylinders unless the pistons 12 of bothmaster cylinders 10 and 11 are advanced simultaneously by operation ofboth pedals.

Further movement of the piston assembly 12 of the master cylinder 10 inthe same direction opens the tipping valve 23 to allow fluid underpressure from the hydraulic accumulator 20 to enter the pressure space15 from whence it is delivered to the brakes on wheels on the side ofthe vehicle supplied by that master cylinder 10 through the connection26.

When the piston assemblies 12 of both master cylinders 10 and 11 areadvanced simultaneously, upon opening of the transfer valves 25, thepressure space 15 of one cylinder is placed in communication with thepressure space 15 of the other and after the tipping valves 23 areopened, fluid supplied to the pressure spaces 15 from the hydraulicaccumulator 20 can pass freely between the pressure spaces to compensatefor uneven wear of the friction surfaces of the brakes on opposite sidesof the vehicles.

It is arranged that closure of the valve 18 and opening of the valve 25of each master cylinder takes place upon initial movement of the cage 19through a relatively small distance to ensure that the transfer valveopens at the earliest possible moment. However, an additional movementof the cage, which is substantial in comparison with the said initialmovement, is required to effect opening of the valves 23. This ensuresthat, when both master cylinders are operated simultaneously, thetransfer valves 25 under all operating conditions are opened before thevalves 23 are opened irrespective of the effect of the differential wearof the brake pedal linkages when pedals for operating the mastercylinders are latched together, or differential wear of the brake pedallinkages which is further accentuated by differential movement of thepedal when unlatched.

In the embodiment of FIG. 2, where corresponding reference numerals havebeen used to indicated corresponding parts, instead of fluid underpressure being supplied directly to the brakes on opposite sides of thevehicle from the pressure spaces 15, the pressure in each pressure spaceI5 acts on the outer end of a secondary piston 30 working in a secondarybore 31 in the master cylinder body. Fluid from an hydrostatic reservoir32 is normally supplied to a secondary pressure space 33 between eachsecondary piston 30 and an adjacent end wall of the cylinder of eachmaster cylinder 10, 11 through a branched line 34, and a radialrecuperation port 35 in each secondary piston. The secondary pressurespaces 33 are connected to slave cylinders 36 of brakes on wheels ofopposite sides of a vehicle through connections 37.

When the pressure space 15 of one master cylinder, for example themaster cylinder 10, is pressurized by the supply to it of fluid underpressure from thepressure source, the pressure fluid in the pressurespace 15 acts on the adjacent end of the secondary piston 30 to advanceit in the secondary bore 31. Initially this movement closes therecuperation port 35 so that pressure builds up in the secondarypressure space 33 in front of the secondary piston 30. Further movementof the secondary piston 30 in the same direction delivers fluid underpressure from the pressure space 33 to the slave cylinder 36 foractuating the brakes on the wheels on the side of the vehicle adapted tobe applied by master cylinder 10.

In the event of failure of the source of fluid under pressure, or thepressure space 15, the piston assembly 12 is adapted to engage theadjacent end of the secondary piston 30 to advance the second piston inthe secondary bore as described above. In this condition, when thepiston assemblies 12 are advanced simultaneously, means are incorporatedfor equalizing the braking effort applied to the brakes on oppositesides of the vehicle to compensate. for uneven wear of the frictionsurfaces. As illustrated these compensation means comprises a shuttlevalve 38 located in a line 39 connecting the connections 37 to the slavecylinders 36. The shuttle valve 38 comprises a valve member 40 workingin a bore 41. The valve member 40 is adapted to be moved in a directionto equalize the pressures applied to the brakes on opposite sides of thevehicle against the force in one of a pair of oppositely acting returnsprings 42 normally holding the valve member 40 in a central position.The construction and operation of the embodiment of FIG. 2 is otherwisethe same as FIG. 1 and need not be further described herein.

The embodiment of FIG. 3 is similar to that described above in FIGS. 1and 2 and corresponding reference numerals have been used to indicatecorresponding parts.

In this construction the pressure space 15 in each master cylinder isconnected through the connection 26 to the slave cylindersof the brakeson the wheels on that side of the vehicle controlled by that mastercylinder, and the secondary pressure space 33 of that cylinder isconnected to the slave cylinders through the connection 37. Each slavecylinder 36 comprises a differential piston 46 working in a stepped bore47 in a cylinder body. In normal operation the pressure from thesecondary pressure space 33 acts on the end of the piston 46 of smallerdiameter and the pressure from the pressure space acts on a step in thepiston 46 at the change in diameter. In a modification the connectionsbetween the pressure spaces and the slave cylinders may be interchanged.

The operation of the embodiment of FIG. 3 is, in the main, identicalwith that described above with reference to FIG. 2. However, in theevent of failure of either of the secondary pressure spaces, the brakeson opposite sides of the vehicle can still be applied independently orsimultaneously by the supply of fluid under pressure to the slavecylinders 36 from one or both pressure spaces 15.

The areas of the differential pistons 46 over which the supplyingpressure acts are chosen such that the forces applied to the-piston 46from the pressure spaces are equal. Altematively, the areas may bechosen such that the forces applied to the piston 46 from the pressurespaces are different.

A practical construction for each master cylinder incorporated in theembodiment of FIG. 3 is illustrated in FIG. 4 of the drawings andcorresponding reference numerals have been used to indicatecorresponding parts. Features of the master cylinder illustrated in FIG.4 form the subject of our pending Pat. application Nos. 28296/68,28297/68, 28298/68, 28299/68 and 16377169, and these features need notbe described further herein.

The master cylinder illustrated in FIG. 4 can be adapted for use in theembodiment of FIG. 2 simply by omitting the outlet connection 26 fromthe pressure space 15. Similarly it can be adapted for use in theembodiment of FIG. 1 by omitting the secondary piston 30, the connection34 from the hydrostatic reservoir and the connection 37 to the brakes.

I claim:

1. A two-pedal hydraulic braking system, comprising in combination:

a pair of master cylinders, each said cylinder including a cylinder bodyhaving a bore and a pedal-operated piston working in said bore;

a first passage in each said cylinder bodyconnected to a source of fluidunder pressure and opening into a primary pressure space defined in saidbore in front of said pistons, connections being provided between saidpressure spaces and brakes on wheels on opposite sides of a vehicle;

a normally closed first valve at each cylinder body controlling saidfirst passage;

a second passage in each said cylinder body leading into said primarypressure space;

a reservoir for the fluid system connected to said second passage;

a normally open second valve at each cylinder body controlling saidsecond passage;

a third passage leading into said primary pressure space in each saidmaster cylinder, the third passage of one master cylinder beingconnected to the third passage of the other master cylinder; and

a normally closed transfer valve at each cylinder controlling said thirdpassage;

said first valve, said second valve and said transfer valve eachcomprising a spring-loaded tipping valve adapted to be actuated by saidpedal-operated piston whereby simultaneous operation of both of saidpistons opens both of said transfer valves to connect both of saidprimary pressure spaces.

2. The invention as claimed in claim 1, wherein each transfer valve isadapted to be opened after closure of said second valve has beeneffected, and before opening of said first valve.

3. The invention as claimed in claim 1 incorporating a separateconnection between said primary pressure space of each master cylinderand slave cylinders of wheel brakes on the side of the vehicle whichsaid primary pressure space is adapted to supply.

4. A two-pedal hydraulic braking system comprising in combination:

two master cylinders, each said master cylinder including a cylinderbody having a bore substantially closed at its inner end, apedal-operated piston working in said bore in said cylinder body, andhaving an inner end, a secondary piston workingin said cylinder bore ina position in advance of and spaced from said inner end of saidpedaloperated piston and having an inner end, a primary pressure spacebeing defined in said cylinder bore between said pistons;

a first passage in each said cylinder body connected to a source offluid under pressure and opening into said primary pressure space;

a normally closed first valve at each cylinder body controlling saidfirst passage;

a second passage in each said cylinder body leading into said primarypressure space;

a reservoir for hydraulic fluid connected to said second passage;

a normally open second valve at each cylinder body controlling saidsecond passage;

a secondary passage space defined in said cylinder bore between saidinner end of said secondary piston and said inner end of said bore;

a normally open third valve providing communication between saidsecondary pressure space and a second reservoir for hydraulic fluid andadapted to be closed when said secondary piston is advanced in saidcylinder bore whereby fluid in said secondary pressure space ispressurized, connections being provided between both pressure spaces ofboth master cylinders and brakes on wheels on opposite sides of saidvehicle;

a third passage at each said master cylinder leading into said primarypressure space, the third passage of one master cylinder being connectedto the third passage of the other master cylinder;

a normally closed transfer valve at each cylinder controlling said thirdpassage; and

means mechanically actuated by said pedal-operated piston for openingsaid transfer valve on axial movement of said piston, wherebysimultaneous operation of both of said pistons opens both of saidtransfer valves to connect both of said primary pressure spaces.

5. The invention as claimed in claim 4 wherein said first valve, saidsecond valve and said transfer valve of each master cylinder eachcomprises a spring-loaded tipping valve and wherein a stern incorporatedin said tipping valve extends into said bore in said cylinder body, eachvalve being adapted to be tipped in an open position by an engagementwith its stem of a part of said pedal-operated piston.

6. The invention as claimed in claim 5, incorporating means forequalizing the pressures in said secondary pressure spaces of saidmaster cylinders to compensate for wear of the friction linings whenboth master cylinders are operated simultaneously.

7. The invention as claimed in claim 6, wherein said means forequalizing said pressures comprises a line connecting said secondarypressure spaces and a shuttle valve located in said line, said shuttlevalve comprising a housing having an openended bore a valve membermovable in said open-ended bore to equalize the pressures, and a pair ofoppositely acting return springs normally holding said valve member in acentralized position.

8. The invention as claimed in claim 7, wherein a separate connection isprovided between each primary pressure space and each secondary pressurespace in each master cylinder and common slave cylinders of brakes onwheels on that side of the vehicle which that'master cylinder is adaptedto supply.

9. The invention as claimed in claim 8, wherein each slave cylindercomprises a housing having a stepped cylinder bore, a

differential piston working in said stepped cylinder bore, and whereinthe pressure from each pressure space of one master cylinder acts on adifferent area of the differential piston.

10. The invention as claimed in claim 9, wherein the pressure in saidsecondary pressure space acts on the end of said differential piston oflesser diameter, and the pressure in said primary pressure space acts onthe face of said differential piston at a step in the change indiameter.

11. The invention as claimed in claim 9, wherein the pressure in saidsecondary pressure space acts on a face of said differential piston at astep in a change in diameter, and the pressure in the primary pressurespace acts on the end of said piston of lesser diameter.

1. A two-pedal hydraulic braking system, comprising in combination: apair of master cylinders, each said cylinder including a cylinder bodyhaving a bore and a pedal-operated piston working in said bore; a firstpassage in each said cylinder body connected to a source of fluid underpressure and opening into a primary pressure space defined in said borein front of said pistons, connections being provided between saidpressure spaces and brakes on wheels on opposite sides of a vehicle; anormally closed first valve at each cylinder body controlling said firstpassage; a second passage in each said cylinder body leading into saidprimary pressure space; a reservoir for the fluid system connected tosaid second passage; a normally open second valve at each cylinder bodycontrolling said second passage; a third passage leading into saidprimary pressure space in each said master cylinder, the third passageof one master cylinder being connected to the third passage of the othermaster cylinder; and a normally closed transfer valve at each cylindercontrolling said third passage; said first valve, said second valve andsaid transfer valve each comprising a spring-loaded tipping valveadapted to be actuated by said pedal-operated piston wherebysimultaneous operation of both of said pistons opens both of saidtransfer valves to connect both of said primary pressure spaces.
 2. Theinvention as claimed in claim 1, wherein each transfer valve is adaptedto be opened after closure of said second valve has been effected, andbefore opening of said first valve.
 3. The invention as claimed in claim1 incorporating a separate Connection between said primary pressurespace of each master cylinder and slave cylinders of wheel brakes on theside of the vehicle which said primary pressure space is adapted tosupply.
 4. A two-pedal hydraulic braking system comprising incombination: two master cylinders, each said master cylinder including acylinder body having a bore substantially closed at its inner end, apedal-operated piston working in said bore in said cylinder body, andhaving an inner end, a secondary piston working in said cylinder bore ina position in advance of and spaced from said inner end of saidpedal-operated piston and having an inner end, a primary pressure spacebeing defined in said cylinder bore between said pistons; a firstpassage in each said cylinder body connected to a source of fluid underpressure and opening into said primary pressure space; a normally closedfirst valve at each cylinder body controlling said first passage; asecond passage in each said cylinder body leading into said primarypressure space; a reservoir for hydraulic fluid connected to said secondpassage; a normally open second valve at each cylinder body controllingsaid second passage; a secondary pressure space defined in said cylinderbore between said inner end of said secondary piston and said inner endof said bore; a normally open third valve providing communicationbetween said secondary pressure space and a second reservoir forhydraulic fluid and adapted to be closed when said secondary piston isadvanced in said cylinder bore whereby fluid in said secondary pressurespace is pressurized, connections being provided between both pressurespaces of both master cylinders and brakes on wheels on opposite sidesof said vehicle; a third passage at each said master cylinder leadinginto said primary pressure space, the third passage of one mastercylinder being connected to the third passage of the other mastercylinder; a normally closed transfer valve at each cylinder controllingsaid third passage; and means mechanically actuated by saidpedal-operated piston for opening said transfer valve on axial movementof said piston, whereby simultaneous operation of both of said pistonsopens both of said transfer valves to connect both of said primarypressure spaces.
 5. The invention as claimed in claim 4 wherein saidfirst valve, said second valve and said transfer valve of each mastercylinder each comprises a spring-loaded tipping valve and wherein a stemincorporated in said tipping valve extends into said bore in saidcylinder body, each valve being adapted to be tipped into an openposition by an engagement with its stem of a part of said pedal-operatedpiston.
 6. The invention as claimed in claim 5, incorporating means forequalizing the pressures in said secondary pressure spaces of saidmaster cylinders to compensate for wear of the friction linings whenboth master cylinders are operated simultaneously.
 7. The invention asclaimed in claim 6, wherein said means for equalizing said pressurescomprises a line connecting said secondary pressure spaces and a shuttlevalve located in said line, said shuttle valve comprising a housinghaving an open-ended bore a valve member movable in said open-ended boreto equalize the pressures, and a pair of oppositely acting returnsprings normally holding said valve member in a centralized position. 8.The invention as claimed in claim 7, wherein a separate connection isprovided between each primary pressure space and each secondary pressurespace in each master cylinder and common slave cylinders of brakes onwheels on that side of the vehicle which that master cylinder is adaptedto supply.
 9. The invention as claimed in claim 8, wherein each slavecylinder comprises a housing having a stepped cylinder bore, adifferential piston working in said stepped cylinder bore, and whereinthe pressure from each pressure space of one master cylinder acts on adifferent area of the differential Piston.
 10. The invention as claimedin claim 9, wherein the pressure in said secondary pressure space actson the end of said differential piston of lesser diameter, and thepressure in said primary pressure space acts on the face of saiddifferential piston at a step in the change in diameter.
 11. Theinvention as claimed in claim 9, wherein the pressure in said secondarypressure space acts on a face of said differential piston at a step in achange in diameter, and the pressure in the primary pressure space actson the end of said piston of lesser diameter.